Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 44: Joint Session "Spins in Organic Materials" (jointly with DS)

MA 44.1: Vortrag

Donnerstag, 29. März 2012, 16:45–17:00, H 1012

Tunneling anisotropic magnetoresistance in organic spin valves — •M. Grünewald^1,3, M. Wahler^1,3, F. Schumann³, C. Gould¹, R. Schmidt², F. Würthner², L.W. Molenkamp¹, and G. Schmidt^1,3 — ¹Physikalisches Institut (EP3) Universität Würzburg, Am Hubland, 97074 Würzburg — ²Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg — ³Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, von-Danckelmann-Platz 3, 06120 Halle

Over the past years a number of spin valves (SV) based on various organic semiconductors (OSCs) and contact materials have been demonstrated. Although some experiments indicate injection of spinpolarized carriers and some clearly show tunneling, it is still unclear for a number of other results whether their data show tunneling magnetoresistance (TMR) or actual spin injection and consequently giant magnetoresistance (GMR). We report the observation of tunneling anisotropic magnetoresistance (TAMR) in an organic SV-like structure with only one ferromagnetic electrode. The device is based on a new perylene diimide-based n-type OSC. The effect originates from the tunneling injection from the bottom contact (La_0.7Sr_0.3MnO₃). Magnetoresistance measurements show a clear SV signal, with the typical two-step switching pattern caused by the magnetocrystalline anisotropy of the epitaxial magnetic electrode. TAMR so far has not been considered when interpreting the results of organic SVs. Our results imply that careful measurements on any organic SV are necessary in order to distinguish between TAMR and true SV-operation (TMR/GMR).